Re: [PATCH v1] ACPI / scan: Acquire device_hotplug_lock in acpi_scan_init()

Michal Hocko
2019-07-26T07:57:32Z

On Thu 25-07-19 22:49:36, David Hildenbrand wrote:
> On 25.07.19 21:19, Michal Hocko wrote:
[...]
> > We need to rationalize the locking here, not to add more hacks.
>
> No, sorry. The real hack is calling a function that is *documented* to
> be called under lock without it. That is an optimization for a special
> case. That is the black magic in the code.

OK, let me ask differently. What does the device_hotplug_lock actually
protects from in the add_memory path? (Which data structures)

This function is meant to be used when struct pages and node/zone data
structures should be updated. Why should we even care about some device
concept here? This should all be handled a layer up. Not all memory will
have user space API to control online/offline state.
--
Michal Hocko
SUSE Labs